The real approach of creating AI for a fighting robot in an MMO
I would set up a list of goals for your bot. These could be 'maintain a minimum level of health', 'knock out human player', 'block way to location X', etc. This obviously depends on the domain of your MMO.

Then you can use a planner to achieve these goals in the game. You define a set of actions with preconditions and effects, set the current goal, and the planner will work out a list of actions for the bot to achieve the goal. You can easily express your actions (and the domain) in PDDL.

Examples for actions would be 'move to location X', 'eat X', 'attack player X'. A precondition of 'attack player X' could be 'health(X) is low', and an effect could be 'health(X) is reduced by Y'. There are different ways of expressing these depending on the planner's capabilities.

The beauty of this is that you don't actually have to explicitly code any behaviour. You describe the domain, and tell the bot what it should achieve, and what capabilities it has. The actual behaviour then emerges out of that description. If the bot only attacks a player if the player has lower health, then observing the player eat (and thus up their health) could result in the bot eating (to push its own health above the player's so that it can attack) &mdash; but you have not told the bot directly to do that.

For a starting point, go to http://education.planning.domains/ for a list of resources.

If you only have a few actions available, it might appear predictable to a human user, but with a variety of goals and actions, this will quickly become more complex and seem more 'intelligent'. 

Update: Here is a link to a paper, Applying Goal-Oriented Action Planning to Games, which describes how this can be applied in a game.